The Linkage Between Methane Fluxes and Gross Primary Productivity at Diurnal and Seasonal Scales on a Rice Paddy Field in Eastern China

Abstract Carbon dioxide (CO 2 ) and methane (CH 4 ) are the most important two greenhouse gases in the atmosphere which were closely coupled between terrestrial ecosystems and the atmosphere. However, the relationship between CO 2 and CH 4 fluxes of rice paddy at different temporal scales is still unclear. Based on 6 years of eddy covariance measurements on a flooded rice paddy field in Eastern China, the relationship between gross primary productivity (GPP) and CH 4 fluxes and the effects of biophysical and environmental factors on daily CH 4 /GPP were investigated. CH 4 fluxes and GPP were tightly linked at diurnal and seasonal scales. On average, half‐hourly CH 4 fluxes lagged GPP by 1.5 hr while daily GPP lagged CH 4 fluxes by 19 days over the growing season. Leaf area index, water table depth (WTD), air temperature, vapor pressure deficit, and canopy conductance significantly affect daily CH 4 /GPP. A semi‐empirical multiplicative model was able to capture 77% and 84% seasonal variability of daily CH 4 /GPP for the training data set and testing data set, respectively. WTD is a crucial input affecting the performance of the model. Without WTD included, the agreement between estimated and observed daily CH 4 /GPP was weakened. Under the condition without WTD data available, separate calibration of the semi‐empirical multiplicative model before and after panicle initiation could improve the estimation of daily CH 4 /GPP to some extent. The findings in this study enhance our understanding regarding the complex interactions between CH 4 fluxes and GPP in the rice paddy and are helpful for better estimation of CH 4 fluxes from GPP.